8 years ago.

3.3V regulator fail

I am working first time on stm32f302r8 dev boards, just purchased 06 no.s, while on first day of working my 03no.s of board get damaged...

In all the boards(damaged) i noticed that regulator of 3.3 v (U4) i.e LD39050pu33 gets damaged while my external voltage input (E5V) at pin no.6 (CN7) is constant regulated 5V d.c and jumper (J5) was in position ( 2 , 3).

I am enough confident that has not did anything wrong , still U4 gets damaged giving output voltage of 1v in 2 boards and 5v in one boards, and the controller IC getting hot at this board, while i have repaired the other two's in which U4 giving 1V or less.. but i am sure that the other board might be not repairable bcoz its controller ic also damged bcoz of that 5v.

Can any body tell me what are the possible cases in which U4 may get damaged, why it happens so, nothing wrong with my hardware design, even i have not used 3.3 v as ouptut to my other circuitry, pin no. 12, 16 of CN7 are not connected to anything else.

Pls suggest me some wayout, otherwise i have no option to put the boards in dump and going ahead with other tools/boards